Acoustical mufflers are generally of the absorptive or reactive type with the reactive type mufflers relying upon self-destruction of the sound waves through reflection or expansion.
Additionally, where the muffler is of the marine type provision is usually made for directing at least a portion of the engine coolant through the exhaust system.
In the reactive type mufflers the construction will usually take the form of either a plurality of interconnected expansion chambers or a series of baffles positioned within the flow path of the exhaust gases to attenuate engine noise.
Typical of the expansion chamber type muffler designs are those shown in U.S. Pat. Nos. 2,511,190; 2,516,948; 3,077,240; 3,080,939; 3,101,811; 3,177,971; and 3,448,824. Of interest with regard to baffle type mufflers are U.S. Pat. Nos. 2,485,555; 2,933,148; and 3,220,506.
The latter patent is assigned to the assignee of the present application and has found wide scale commercial use, although in its present commercial form the baffles are reversed with respect to the flow of fluid through the muffler from the direction shown in the patent.
Despite the variety of muffler designs which presently exist, many of them for marine use and some, such as applicant's present commercial design, having met with substantial commercial success, a need still exists for a marine muffler which will provide improved sound attenuation over a substantially broad spectrum and with a substantially lower dB (A).